1. Field of the Invention
The present invention relates to a scroll compressor, and more particularly, to an outer rotor type scroll compressor.
2. Description of the Related Art
Generally, a scroll compressor is a device for compressing a fluid kept in a compression chamber by varying a volume of the compression chamber constructed with movable and fixed scrolls by rotating the orbiting scroll. The scroll compressor has an efficiency greater than that of a reciprocating or rotary compressor, small vibration, and low noise, and can be made light in weight. Hence, the scroll compressor is used in various fields nowadays.
Constitution and operation of a scroll compressor according to a related art are explained by referring to the attached drawings as follows.
Referring to FIG. 1A, a scroll compressor according to a related art includes a compressor housing 1, a crankcase 2, an inner rotor type motor 3, a crankshaft 4, an orbiting scroll 5, and a fixed scroll 6.
The compressor housing 1 forms an exterior of the compressor, and various components are provided in the compressor housing 1.
The crankcase 2 is fixed inside the compressor housing 1. A boss 2a protrudes downward from a central portion of the crankcase 2, and a bearing hole 2b penetrates a center of the boss 2a. 
The inner rotor type motor 3 is provided at a lower side of the crankcase 2, and includes a rotor 3a and a stator 3b. The rotor 3a, as shown in FIG. 1A, is fixed to a circumference of the crankshaft 4 to revolve together with the crankshaft 4. The stator 3b is fixed inside the compressor housing 1. And, the rotor 3a is positioned in a hollow central portion of the stator 3b so that an inner circumferential surface of the stator 3b is spaced by a predetermined interval from an outer circumferential surface of the rotor 3a. 
The crankshaft 4 is coupled with the rotor 3a to revolve together. One side of the crankshaft 4 is configured to penetrate the bearing hole 2b formed in the crankcase 2. And, an eccentric pin 4a is formed at an upper end of the crankshaft 4 near the crankcase 2. Further, a bearing is provided between the bearing hole 2b and the crankshaft 4 to guarantee smooth rotation of the crankshaft 4.
The orbiting scroll 5 is coupled with the eccentric pin of the crankshaft 4 to rotate.
The fixed scroll 6 is coupled with the crankcase 2 to be fixed thereto, and provides a compression chamber 6 with the orbiting scroll 5 to compress a fluid confined in the compression chamber 6a. 
Meanwhile, the scroll compressor according to the related art further includes a plurality of counterweights canceling out an eccentric force generated when the orbiting scroll 5, eccentric from a rotation center, and the eccentric pin 4a of the crankshaft 4 are rotating. The counterweights, as shown in FIG. 1A, include an upper counterweight 7 provided in a direction opposite to an eccentric direction of the eccentric pin 4a of the crankshaft 4 and a lower counterweight 8 provided in the same direction of the eccentric direction of the eccentric pin 4a of the crankshaft 4 near a bottom of the rotor 3a. 
Referring to FIG. 1B, the scroll compressor according to the related art can further include a sub-frame 9 as well as the above-explained elements. The sub-frame 9 is provided at a lower side of the crankshaft 4. One side of the sub-frame 9 is fixed to an inner lower side of the compressor housing 1 to support a bottom of the crankshaft 4, thereby preventing the crankshaft 4 from falling due to gravity.
Referring to FIG. 1C and FIG. 1D, the scroll compressor according to the related art has an oil supply path for smooth lubrication of rotational and frictional portions and a return structure for returning the supplied oil. And, they are explained briefly in the following.
First of all, oil 1b is stored in an inner lower side of the compressor housing 1.
A lower end of the crankshaft 4 is positioned to dip in the stored oil 1b, and an oil supplying path 4b is formed inside the crankshaft 4 to be inclined in a direction extending farther from the rotation center of the crankshaft 4 toward an upper side.
Moreover, an oil return path 2c is formed in the crankcase 2 to penetrate from a central portion to one side of the crankcase 2, and is formed for returning the oil 1b, which has been supplied to the center of the crankcase 2 through the oil supplying path 4b, to a lower side of the compressor housing 1.
Further, an oil path 1a, as shown in FIG. 1C and FIG. 1D, is formed between an inner face of the compressor housing 1 and an outer circumferential surface of the stator 3b to guide the oil 1b drained through the oil return path 2c to the lower side of the compressor housing 1.
The above-constituted scroll compressor according to the related art operates as follows.
First of all, power is applied to turn the rotor 3a and crankshaft 4, and then the turning crankshaft 4 revolves the orbiting scroll 5 coupled with the eccentric pin 4a. As the orbiting scroll 5 revolves, a fluid locked inside the compression chamber formed between the fixed and orbiting scrolls 6 and 5 becomes compressed.
Simultaneously, while the crankshaft 4 turns, the oil 1b in the lower side of the compressor housing 1 is elevated along the oil supplying path 4b by a centrifugal force to lubricate the bearing unit at a side of the crankcase 2. Most of the supplied oil 1b is returned to the lower side of the compressor housing 1 along the oil return path 2c and the oil path 1a to be kept in store.
However, the above-constituted scroll compressor according to the related art has the following problems or disadvantages.
First of all, the rotor 3a provided at the lower side of the crankcase 2 is fixed to the circumference of the crankshaft 4 and the crankshaft 4 is provided to penetrate the bearing hole 2b formed in the center of the boss 2a of the crankcase 2. Hence, the boss 2a of the crankcase 2 and the rotor 3a occupy the spaces at upper and lower sides of the crankshaft 4, thereby setting structural limitation on reducing the height of the machine.
Secondly, the upper counterweight 7 is provided in the direction opposite to the eccentric direction of the eccentric pin 4a of the crankshaft 4 over the rotor 3a to be disposed between the boss 2a of the crankcase 2 and the top surface of the rotor 3a. Hence, the height of the machine increases additionally.
Thirdly, the inner rotor type motor 3 has the rotor 3a located inside the stator 3b. And, an outer diameter of the inner rotor type motor 3 is smaller than that of an outer rotor type motor having a rotor placed outside a stator. In order to cancel out the eccentric force when one angular speed ω of the counterweight is equal to the other under the same condition, a mass m should be increased to be inversely proportional to a distance r between a rotation center and a weight center of the counterweight using the equation of ‘F=mrω2’ for finding a centrifugal force of the counter weight. Hence, the size, i.e. height, of the counterweight should be increased to increase the mass with the same material, whereby the height of the machine is increased more to enhance the structural limitation together with the above-explained second problem of the related art.